The world’s smallest FM radio transmitter – made from graphene

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The heart of every radio transmitter is a reliable oscillator. Creating small, and tunable, oscillators that can maintain a precise frequency when conditions like temperature, pressure or humidity change, can be challenging. Engineers from Columbia University have just revealed to us the world’s smallest FM transmitter, which they managed to build around a nanoscale graphene oscillator. Details of their device have just appeared in the current online issue of Nature Nanotechnology.

Standard oscillators used in radios today are typically macroscopic resonators made from quartz crystals that require significant “off-chip” board space. The Columbia researchers have now blown that concept out of the water by creating atomically thin nano-electro-mechanical (NEM) resonators that can be tuned within a respectable 14% range. Their device was fabricated using a small graphene element suspended within a clamp made from SU-8 photoresist. SU-8 is a viscous polymer that can be processed with standard contact lithography and patterned into high aspect ratio structures.

When they integrated their device into a VCO (voltage-controlled oscillator), a standard component in frequency synthesis, they were able to demonstrate frequency stability and modulation bandwidth sufficient to carry FM signals. Their first successful demonstration was an audio recording of Gangam Style, which despite a fair bit of background noise was quite recognizable, if not entirely pleasing.

The tuning range of most VCO’s is usually somewhere in the range of a few parts per million over a control voltage range of 0 to 3 volts. That’s good enough to act as the timeclock in a computer. Applications for miniature size transmitters, like for implants, may not be quite so demanding. The issues for devices inside the body may be more about getting sufficient transmission energy at the right frequency. The Columbia device was designed for operation in the 100 megahertz range, while the ideal range for transmitter signals through the aqueous tissue environment is still very much under study.

This week alone there have been several completely novel applications for graphene unleashed to the world at large. Not least among them is another story in Nature Nanotechnology describing the use of graphene nanribbons as genetic sequencing pores. We have talked previously about this technology and its potential to revolutionize personal medical awareness. Graphene has also been shown in recent times to potentially be an ideal material for fashioning microscale antennas, or graphenas, if you will. While these advances are each independently noteworthy, the real excitement may come if and when they are eventually integrated. A graphene pore sequencer, transmitting data using a graphene-based oscillator coupled to a graphene radiator would make quite a headline.

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